Continuous gas analyzer



Feb. 16, 1960 s, KATZ ETAL 2,925,327

CONTINUOUS GAS ANALYZER Filed March 13. 1958 2 Sheets-Sheet 1 REAGENT GAS SAMPLE GAS FLOW FLOW CONTROL CONTROL SYSTEM SYSTEM YMIXER- 7 REACTOR FLOW-RESPONSIVE OR PREssuRE-REsPoNswE r INSTRUMENTATION 6 (RECORDING IN I Y MOLE PERCENT) CONSTRICTION ICHEM'ICAL TRAPS IN VEN TORS Feb. 16, 1960 v s. K-ATZ ET AL 2,925,327

7 CONTINUOUS GAS ANALYZER Filed March 13, 1958 2 Sheets-Sheet 2 16 REAGENT GAS 14 SAMPLE GAS 2 APT DBM

SODA LIME SILICA GEL CALCIUM SULFATE APT @100 I /10 APT 7 97 98 G 99 v A ,u 12

ELECTRONIC INVENTORS PRESSURE M'CROMAX TRANSDUCER RECORDER By Sjdney .Kafz a 108 Charles W. Weber ATTORNEY lubrication, and frictional binding.

, mol pe nt of a selsts "randomly varying" amounts of It is another object ofth Figure 1 isa si i Figure 2 system of Figure 1."

' are che ally -c n ed Ionian qont a us s s lreag'ent'j'gas and the samp I reaction; zone at zpreselect 'i This invention relates'toa novel'proeesswandapparatus for continuously, accurately, and dynamically measuring the concentration of one, selectedng as in a flowing gas mixture, and more especially to a'procese and apparatus adapted to provide precise measurementsof concentra- 1 tion of the selected gas despite the presence of randomlyvarylng amounts of othergasesin'the mixture if] There are many disadvantages in the use of known batch systems for intermittent analysis ofgas mixtures;

' In these systems a reciprocatingrpump; is used tomo-f mentarily isolate ,abateh of g as, 'another gas is added, and the change in volume of the gas mixture being analyzed is madeto indicate thepercentageof the desi'red constituent; For example, anpum'p system requiresthe considerations of leaks, corrosion, mechanicalfailure, V I I Moreover, where 'gases must be handled at reduced or atjel'evated temperatures, the dimensional tolerances inpurnp-coinponents become acritical matter. ln addition, since the response froma pump systemis truly intermittent in nature, it

containsmore inherent-lag than does a dynamireeponse sy e In our improved system, we have overeomethe above disadvantages providing a i which heflss st l li rat {automatically over long an y appara us; an p ide a anal z r r. m

analyzer which will respon pidly to gfros'sfchanges in the content ofthe selected 'gas under analysis; W

It is still another objectof'this'. inyentiontoiprovi'de an a r for meas in he s e ed' a cionq i ati is calibrated in terms the samplefgas.--

, 2 Referring to Figure flue 'ne mthesample gas 'conib ine"in' the reaction to foima' productg asl the reagent being preselectedto providea reaction wherein thenumberof moles cr me greener; gas-is difierent "from; the sum or: the males of the: react-ants; The prod-u gasaiid anyunreacted gases are-withdravvn continubusl'yifrom the'reaction zone, and

the exit 'gas' stream is nionitorerl continuously'to-provide an indication of the molar'flow -rat'e thereof. The difi'erence in the total molar rates of flowinto and out of e the reaction zonei is; then "directly related'to' thefluorine content OfthesampIe gas. Consequently, the analyzer of the fluorine concentration in l reference'numeral Idesignates aninput line for asample gas and numeral 3 is aninpu't line for a reagentgas sample gasis fed to a flow "control system "4 and: the reagentgas is fe'cl to new control system 5. These systems maintain preselected molor flovv rates of thcrjgasesi A helical tube or any other suitable mixer-reactor 1Iis connected to receive th ut t sm; flQ 'ifq t i s t and A capillaryor other suitable flow 'constriction" 6 is connected to receive the outputfromi the-reactor 1. Conuected'into the'outlet line of the reactor 1 is an instru mer1tation system 7 which is responsive to molarfrate of flow or,:'alternatively,ito pressure. The instrumenta t n. sys em 7 is sa br ts w th s mp gas s of new fl brin c nt to; r q j te m f, o P r en p o ec i e hem cal traps] t t n e f a va m hi lmp 9. Thevacuum pumplis adaptedto maintain r:

ii an aai ac 4 V v r H y ik ie t nahaw, te isursg, th flow 99??? te s taatlpiiah l The, output of the trans continuously and automatically over long periods a minimum of zero dri ft .j ,t v T ese and other obje andaa v 'nt e sft is i v nt n willbe app en f o nia c ns dsratinpfth detai ed t j description l owin n ect o wit v t isldmw n s,

wherein:

nd; M V, isa more detailed schema Briefly, the operation to v lyzer, as. illustrated with fluorine-"gasyis as follows: A

reagent gas and v a sample of thefiuorine-containing,gas

action zone maintained at r a selected, te

r lp 'd 'sqh'eaa'tejqaa am of 211 Qftinuous analyzer utilizing: principles o f the invent' V, sw at; e e s "overgs pic ms u aui' t l ts o reaction with the fluorine." The rea ent-gas andtlie v-" sran ive it s me tio '1 a e The samplegas fed through shownin nio'reid'e .line 2, va1ve 14 and line 17 to a press ure control-"valve 18. The flow thr ugh valve 183is'regulated by an absolute pressure transiiiittrfg-Zt),"so that the-valve 18 has .an' output through line'25 of a substantially constant pressure. The transmitter go h h 1' 7. -:}23 from a pressure probe pr' de an inpnt t hrou to a control mechanism, I w U valve 18 to thus 'controlthe flow through theyaIve to maintainaconstant pressure output. The control "rneclt I V anism, in the'valve'lfiis conn'ct'ed through a line '24 to a {ce en i ressnre' source such *as a hand blind multiplier 19,,

Theoutput "from the pressure"control yalve 1 8 is 'fed 7 throughflin 25,va'l've- 2'6, line30, capillary 31', line 32,

valve '33 anel fline flto apressure' c'ontrol'valve 35,

' ;Thef ,cofi" trol valve 35 'is* regulated by the. "differential transmitter '3 *vvhich has an input'trom a constant air 9supp1y as a ea diflierentia'l inputfrom lines 39 and 40' 7 connected,across theicapillary 31. The output trom the transmitter is fed'throtigh'line- 41m 9. control mecha- 'nisni in thelcontrol-valve 35. Thiscontrgl mechanism is a so-connected througha line '42- to a constant pressure E'soureej-filir Th' output from the control .valve 35' yjtht'ough'linelfisito thereactor '1. The line -17 conlfnectedby' a linej44gto a meter '45, line; 34 v is 1 connected -by"a}lin 46 to snide 47, and line'41 isconnected-byeline 48 0 amet'er 4 9. These-meters giveaiready' indi i t the pressure conditionsat variousstages-"in sa s. H y n the flowcontrol -'system.; Line 25 4's connected .bylin'e The reagent gas is fed through a flow control system identical to that through which the sample gas is feds The reagent gas is fedthrough line 3, valve 51, line 52 to pressure control valve 53. The output of valve 53-is fed through line 60, valve 61, line 65, capillary 66, line 67, valve 68 and line- 69'to pressure control valve 70. The output of valve 70 is fed throughline 78: to the input of the mixer-reactor. Line 60 is connected through line 58 to the absolute pressure transmitter 55. A source of constant air supply 56 is also connected to transmitter 55. The output of transmitter 55 is connected through line 57 to the control mechanism of valve 53, saidcontrol mechanism also being connected by line 59 to a reference source of pressure 54. A bypass around valve 61, capillary 66 and valve 68 is effected by a line62, valve 63 and line 64. Lines 74 and 75 connected across capillary 66 provide an input to the diiferential transmitter 72 which also has an input from a constant air supply 73. The output of transmitter 72 is connected by a line 76 to a control mechanism in the pressure control valve 70, said control mechanism also being connected by a line 77 to a source of reference pressure 71. Line 69 is connected by a line 79 to a meter 80, and line 76 is connected by a line 81 to a meter 82.

The inlet pressure control valves 18 and 53 regulate the metering pressure to the capillaries 31 and 66, respectively. The pressure'control valves 35 and 70 regulate the flow by receiving the output of the differential pressure transmitters 37 and 72, respectively, applied across the metering capillaries 31 and 66, respectively. The

constancy of the metering (absolute) pressure and the measuring and controlling of the differential pressure across the capillary which is not aifected by the, density of the gas mixture, establishes a. suitable flow-control .system.

The control of the standard volumetric flow bycontrolling the AP (pressure drop across the capillary is defined as follows: a

where V V ,=standard volumetric flow Pl=pressure at capillary inlet P2=pressure at capillary'outlet AP=pressure drop across the capillary n=viscosity of the gas K is a constant, e V I Since the temperature and the capillary dimensions are maintained constant, the important variables affecting the flow rate are gas viscosity, sum of pressures (Pl-i-P2) Cit and AP. However, the instrumentation of the flow control systems (Figure 2) is adapted to maintain'relatively constant P1 and P2 pressures and to control the value of AP .whichis very smallcompared tothe values of P1 and P2. Since a capillary type flow control is affected by gas viscosity, some flow fluctuation may be expected for mixtures of more than two gases. However this fluctuation is often small for the reason thatthe viscosity of fluorine approximates that of most of the'other gases expected in'the sample mixture. Since, the AP, the sum of the pressures P1 and P2, and n are relatively constant, the flow control system. set forth above will yield the required constant standard .volurnetric flow Q,,.

The output gas stream of: the;reactorJ'inFigureZ is fed throughline '86,: flowconstrictiQn 6, line 87 and valve 88 to, the chemical traps 8. The output of the traps 8 is fed 'through line 89, valve 90, line'91-to the inlet of avacuum pump'9. w The vacu li pump. is adapted V -sorptiori ofthereact'o r exit gas.-' i

to maintain a constant pressure at the exit end of the constriction 6. Line 91 is connected by a line 92 and valve 93 to a bleed line 94.

The output pressure of the reactor 1 is also fed by lines 86 and 95, valve 97 and line .98 to an absolute pressure transmitter 10. A branch line 96 from line is connected to an absolute pressure'transmitter 13. Trans-v mitters .10 and 13 are connected to a source of constant air supply 99 and 100, respectively. The outputs of transmitters 10 and 13 are connected by lines 101 and 102 and valves l03 an d 104, respectively, to a common line 105 which is connected to a meter 106. Line 101 is also connected by a line 107.to an electronic pressure transducer 11 which is connected by a line 108 to a micro max recorder 12. Recorder 12 is calibrated in mole percent fluorine.

The transmitter 10 is designed to operate in the normal expected range of concentrations andis normally connected in the system. The transmitter 13,is designed to encompass the range of transmitter 10 and is used when the system is operating outside (above or below),the range of transmitter 10 and also when the system is being checked for leaks. v

Sulfur dioxide (S0 was selected to bathe reagent gas, yielding sulfurylfluoride (SO F as the product gas in accordance with the following reaction:

SCH-P 950 1 1 Preferably, the reactorcis operated at a temperature in excess of C. to ensure complete reaction of the S0 and F but care should be taken to avoid operating at too high a temperature which would cause decomposition of other gases in the mixture if his desired to later utilize such other gases, and to avoid any appreciable reaction between such gases and S0 The input flows to the reactor can differ radically provided that the selected flow rates are maintained constant, that a sufiicient excess of reagent is employed, and thatthe flows are in proper relation to the reactor volume'to ensure'a suitable residence time.

The use of S0 as th e reagent to be reacted with F is not a critical requirement of the fluorine analyzer- Carbon .monoxide. and ethylene are examples of the several otherreagent gases which could be employed with acceptable results. Sulfur dioxide is, however, a particularly suitable reagent for fluorine -analysis,..since S0 does not react appreciably with F, at'low temperatures Moreover, S0 reacts with P to git/e a product gas-which is relatively .inert, and the reaction is quantitz'itive,v Inpensates for variations in sample viscosity (if capillaries are employed) or for variations in molecular weight (if orifice-type constrictions are employed).

In. thearrangement of Figure Z, the pressure in the re actor outlet line is measured by comparing the pressure upstream of the capillary 6 with a selected datum pressure enclosed within the transmitter 10 (or 13). It should be apparentthat a suitable alternative would be to measure .thepressure'difierential across the capillary itself. It should beapparent also that the analyzeris not limited to a pneumatic indicationoffconcentration., If desired, the fluorine concentrationlcould be determinedby monitoring the dielectric constantor the infra-red ab- While the subject analyzer has been described herein in termsof the analysisof F it is apparent that the analyzer could as readily be adapted for the analysis of S0 with F being employed as the reagent gas. In other applications, Br could be used as a reagent gas for the rather than limitation, and it would be apparent that the v invention is equally applicable in fields other than those described.

What is claimed is:

1. An improved system for continuously measuring the concentration of a selected gas ina gas mixture, comprising a first constant volumetric flow control system, means for continuously feeding a sample gas mixture to said first system, a second constant volumetric flow control system, means for continuously feeding a reagent gas to said second system, each of said first and second flow control systems comprising a first pressure control valve, an absolute pressure transmitter connected to the output of said valve to regulate said first valve, a second pressure control valve, a first constriction connected between said control valves, a differential pressure transmitter connected across said first constriction,

the output of said differential pressure transmitterbeing connected to regulate said second pressure control valve, a mixer-reactor operating at a preselected temperature, means for feeding the outputs of said first and second systems to said mixer-reactor, the reagent gas and selected gas being characterized by forming a vdifferent number i of moles of product gas than the sum of the moles of said reagent and selected gases, a second constriction having an input and an output, said second constriction input being connected to the output of the mixer-reactor, evacuation means connected to the output of said second constriction, and a flow-responsive indicating device connected to said mixer-reactor output, the How rate indicated being a measure of the concentration of said selected gas in said References Cited in the file of this patent UNITED STATES PATENTS Vayda et al Jan. 10, 1939 Nier Oct. 30, 1951 Haines et al. Apr. 22, 1952' 

1. AN IMPROVED SYSTEM FOR CONTINUOUSLY MEASURING THE CONCENTRATION OF A SELECTED GAS IN A GAS MIXTURE, COMPRISING A FIRST CONSTANT VOLUMETRIC FLOW CONTROL SYSTEM, MEANS FOR CONTINUOUSLY FEEDING A SAMPLE GAS MIXTURE TO SAID FIRST SYSTEM, A SECOND CONSTANT VOLUMETRIC FLOW CONTROL SYSTEM, MEANS FOR CONTINUOUSLY FEEDING A REAGENT GAS TO SAID SECOND SYSTEM, EACH OF SAID FIRST AND SECOND FLOW CONTROL SYSTEMS COMPRISING A FIRST PRESSURE CONTROL VALVE, AN ABSOLUTE PRESSURE TRANSMITTER CONNECTED TO THE OUTPUT OF SAID VALVE TO REGULATE SAID FIRST VALVE, A SECOND PRESSURE CONTROL VALVE, A FIRST CONSTRICTION CONNECTED BETWEEN SAID CONTROL VALVES, A DIFFERENTIAL PRESSURE TRANSMITTER CONNECTED ACROSS SAID FIRST CONSTRICTION, THE OUTPUT OF SAID DIFFERENTIAL PRESSURE TRANSMITTER BEING CONNECTED TO REGULATE SAID SECOND PRESSURE CONTROL VALVE, A MIXER-REACTOR OPERATING AT A PRESELECTED TEMPERATURE, MEANS FOR FEEDING THE OUTPUTS OF SAID FIRST AND SECOND SYSTEMS TO SAID MIXER-REACTOR, THE REAGENT GAS AND SELECTED GAS BEING CHARACTERIZED BY FORMING A DIFFERENT NUMBER OF MOLES OF PRODUCT GAS THAN THE SUM OF THE MOLES OF SAID REAGENT AND SELECTED GASES, A SECOND CONSTRICTION HAVING 